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Tue, 06 Oct 2026 04:44:19 -0700 (PDT) From: Yiming Qian To: security@kernel.org, mptcp@lists.linux.dev Cc: matttbe@kernel.org, martineau@kernel.org, geliang@kernel.org, netdev@vger.kernel.org, stable@vger.kernel.org, yimingqian591@gmail.com Subject: [PATCH net] mptcp: pm: in-kernel: fix C-flag endpoint accounting on family mismatch Date: Tue, 6 Oct 2026 11:42:27 +0000 Message-ID: <20261006114409.117190-1-yimingqian591@gmail.com> X-Mailer: git-send-email 2.50.1 Precedence: bulk X-Mailing-List: mptcp@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" fill_local_addresses_vec_c_flag() clears the endpoint ID bit in id_avail_bitmap before checking whether the endpoint's address family matches the remote ADD_ADDR. If it does not match, the loop skips the endpoint without incrementing local_addr_used, leaving id_avail_bitmap and local_addr_used inconsistent. Removing that SUBFLOW endpoint later calls __mark_subflow_endp_available(), which sees the cleared bit, expects local_addr_used to be non-zero, and triggers a WARN and, with panic_on_warn=3D1, a panic. Keep the endpoints that are skipped during this specific C-flag iteration available by tracking them in a local bitmap passed to select_local_address(), instead of clearing their IDs in the per-socket bitmap. Only IDs of endpoints actually used for a subflow are now cleared and accounted for. Fixes: 4b1ff850e0c1 ("mptcp: pm: in-kernel: usable client side with C-flag") Cc: stable@vger.kernel.org Signed-off-by: Yiming Qian --- net/mptcp/pm_kernel.c | 22 ++++++++++++++++------ 1 file changed, 16 insertions(+), 6 deletions(-) diff --git a/net/mptcp/pm_kernel.c b/net/mptcp/pm_kernel.c index 1a77508132354..a5952dd0ae125 100644 --- a/net/mptcp/pm_kernel.c +++ b/net/mptcp/pm_kernel.c @@ -120,6 +120,7 @@ static bool has_subflow_daddr(const struct mptcp_sock *= msk, static bool select_local_address(const struct pm_nl_pernet *pernet, const struct mptcp_sock *msk, + const unsigned long *skip, struct mptcp_pm_local *new_local) { struct mptcp_pm_addr_entry *entry; @@ -135,6 +136,9 @@ select_local_address(const struct pm_nl_pernet *pernet, if (!test_bit(entry->addr.id, msk->pm.id_avail_bitmap)) continue; =20 + if (skip && test_bit(entry->addr.id, skip)) + continue; + new_local->addr =3D entry->addr; new_local->flags =3D entry->flags; new_local->ifindex =3D entry->ifindex; @@ -401,7 +405,7 @@ static void mptcp_pm_create_subflow_or_signal_addr(stru= ct mptcp_sock *msk) =20 if (signal_and_subflow) signal_and_subflow =3D false; - else if (!select_local_address(pernet, msk, &local)) + else if (!select_local_address(pernet, msk, NULL, &local)) break; =20 fullmesh =3D !!(local.flags & MPTCP_PM_ADDR_FLAG_FULLMESH); @@ -574,22 +578,28 @@ fill_local_addresses_vec_c_flag(struct mptcp_sock *ms= k, u8 endp_subflow_max =3D mptcp_pm_get_endp_subflow_max(msk); struct sock *sk =3D (struct sock *)msk; struct mptcp_pm_local *local; + DECLARE_BITMAP(skip, MPTCP_PM_MAX_ADDR_ID + 1); int i =3D 0; =20 + bitmap_zero(skip, MPTCP_PM_MAX_ADDR_ID + 1); + while (msk->pm.local_addr_used < endp_subflow_max) { local =3D &locals[i]; =20 - if (!select_local_address(pernet, msk, local)) + if (!select_local_address(pernet, msk, skip, local)) break; =20 - __clear_bit(local->addr.id, msk->pm.id_avail_bitmap); - - if (!mptcp_pm_addr_families_match(sk, &local->addr, remote)) + if (!mptcp_pm_addr_families_match(sk, &local->addr, remote)) { + __set_bit(local->addr.id, skip); continue; + } =20 - if (local->addr.id =3D=3D msk->mpc_endpoint_id) + if (local->addr.id =3D=3D msk->mpc_endpoint_id) { + __set_bit(local->addr.id, skip); continue; + } =20 + __clear_bit(local->addr.id, msk->pm.id_avail_bitmap); msk->pm.local_addr_used++; msk->pm.extra_subflows++; i++; --=20 2.34.1